1. Field of the Invention
The present invention relates to an addition-curable silicone resin composition that can be used favorably for sealing LED elements and the like, and relates particularly to a silicone composition that yields a cured product with superior surface tackiness and favorable strength characteristics, and a cured product of such a composition.
2. Description of the Prior Art
Silicone rubber compositions form cured products that exhibit excellent properties of weather resistance and heat resistance and the like, as well as superior rubber-like properties such as hardness and elongation, and they are consequently used in a wide variety of applications, but because they also exhibit surface tackiness, dust adhesion becomes a problem when such silicone rubber compositions are used as coating agents or the like for electrical or electronic components.
Silicone varnishes exhibit no surface tackiness, meaning dust adhesion is unlikely, but a significant problem arises in that because they lack adequate shock resistance, they tend to be prone to cracking, particularly when exposed to thermal shocks.
In addition-curable silicone rubber compositions, the addition of a resin-like organopolysiloxane component to improve the strength of the cured product is a commonly known technique (patent reference 1). However, even in those cases where the strength of the cured product is raised, surface tackiness and dust adhesion remain problems.
Silicone rubbers attract attention as coating materials for sealing or protecting LED elements as they have good light-resistance. In a white LED device a blue light emitting LED element is covered with a silicone resin layer containing a phosphor. The wavelength of blue light emitted from the LED element is shifted to that of pseudo-white light. Such a silicone layer is formed from an addition-curable silicone rubber composition to which a phosphor has been added. Thus, pseudo-white light with excellent color rendering properties can be obtained. However, if settling of the phosphor occurs within the composition, then variations develop in the color rendering. As a countermeasure, a method has been proposed in which a nanosilica is added to prevent this settling from occurring (patent reference 2).
Furthermore, in order to resolve these problems, it is desirable that the material is able to be readily molded using a conventional molding apparatus such as a transfer molding, compression molding, or injection molding apparatus.
As a result, a silicone composition capable of forming a cured product within a package of electrical or electronic components or the like, wherein dust does not adhere to the surface of the cured product, and the cured product exhibits excellent levels of crack resistance and shock resistance, is keenly sought. Furthermore, a composition that is a solid or semisolid at room temperature (namely, 20° C.±10° C.), and is able to be cured using a conventional molding apparatus would be particularly desirable.
Examples of the conventional technology relating to the present invention include the publications below.
[Patent Reference 1] Japanese Laid-open publication (kokai) No. 2001-002922
[Patent Reference 2] Japanese Laid-open publication (kokai) No. 2005-76003